1. Field of the Invention
The present invention relates to a surface-emitting device and a liquid crystal display apparatus including the surface-emitting device.
2. Description of the Related Art
As a surface-emitting device, a back light or a front light of a reflective liquid crystal display apparatus included in a portable electronic appliance, such as a mobile phone, is known.
Such a known front light is a unit including a light source, an intermediate light-guiding body, a light-guiding plate, and a case for containing these components, whose inner surfaces are reflective.
FIG. 16 is a perspective view of a known liquid crystal display apparatus having such a structure.
The liquid crystal display apparatus illustrated in FIG. 16 includes a liquid crystal display unit 120 and a front light 110 disposed on the front side of the liquid crystal display unit 120 (for example, refer to US Patent No. 20030174491). Details of the structure of the liquid crystal display unit 120 are not shown in the drawing. The liquid crystal display unit 120 is a reflective liquid crystal display unit that displays an image by reflecting light that enters through the front surface. The liquid crystal display unit 120 includes a liquid crystal layer interposed between an upper substrate 121 and a lower substrate 122, wherein the substrates face each other. The liquid crystal display unit 120 displays images by controlling the alignment of the liquid crystal layer so as to change the transmission state of light.
The front light 110 includes a flat light-guiding plate 112, a cylindrical intermediate light-guiding body 113 disposed on an end surface 112a of the light-guiding plate 112, and light-emitting elements 115 and 115 disposed on both longitudinal ends of the intermediate light-guiding body 113. A plurality of protrusions 114 each having a wedge-shaped cross-section is provided on the upper surface of the light-guiding plate 112. The protrusions 114 are disposed parallel to each other to form a prismatic structure.
In the front light 110, light beams emitted from the light-emitting elements 115 and 115 travel through the intermediate light-guiding body 113 to end surface 112a of the light-guiding plate 112 and are guided into the light-guiding plate 112. Then, the light beams are reflected at the inner side of the upper surface of the protrusions 114 on the light-guiding plate 112 in a manner such that the traveling direction of the light beams is changed. As a result, the light beams are emitted downward from the light-guiding plate 112 toward the liquid crystal display unit 120, as illustrated in the drawing.
The known front light 110 is designed so that the total length L of the intermediate light-guiding body 113 and the light-emitting elements 115 and 115 disposed on ends of the intermediate light-guiding body 113 is longer than the width W of the light-guiding plate 112. This design is employed because if the length L is the same as the width W, triangular dark regions 118 and 118, as illustrated in FIG. 17, are formed on the front light 110. These dark regions 118 and 118 are formed because both ends in the width direction of the light-guiding plate 112 are not adjacent to the intermediate light-guiding body 113 and thus the end regions of the light-guiding plate 112 do not receive light from the intermediate light-guiding body 113. Such dark regions 118 and 118 on the light-guiding plate 112 cause a decrease in the uniformity of the amount of light emitted from the surface of the light-guiding plate 112. As a result, the liquid crystal display unit cannot be illuminated uniformly and brightly and the visibility of the liquid crystal display apparatus is reduced.
The formation of dark regions on the light-guiding plate 112 are prevented by setting the length L longer than the width W, as illustrated in FIG. 16, so that the light-emitting elements 115 and 115 protrude outward from the ends in the width direction of the light-guiding plate 112.
There has been a demand for a reduction in size of a surface-emitting device so that the size of portable electronic appliances, such as mobile phones and portable game machines, can be reduced and various functions can be added to such portable electronic appliances.
However, it has been difficult to meet this demand since, as described above, the overall width of a known surface-emitting device is larger than the width of the light-guiding plate because the light-emitting elements are disposed at the ends of the intermediate light-guiding body at positions further outward than the edges of the light-guiding plate in the width direction. When such a surface-emitting device is mounted in a portable electronic appliance, dead space is formed because of the protruding light-emitting elements.
In another known surface-emitting device, as illustrated in FIG. 18, a plurality of light-emitting diodes (LEDs) 215 is disposed on a light-entering surface 212a of a light-guiding plate 212 to directly guide the light from the LEDs 215 to the light-guiding plate 212. In such a known surface-emitting device, the area near the LEDs becomes extremely bright, causing unevenness in luminance in the vicinity of the entering surfaces 212a. Since this region S with uneven luminance has to be disposed so that it is not included in the display region of the liquid crystal display apparatus, even more dead space is formed compared to the above-described surface-emitting device including the intermediate light-guiding body 113.